elm_interface_scrollable: fix wrong mirrored calculation

elm_interface_scrollable: fix wrong mirrored calculation

Summary:
This Patch is regarding D2553, but funtionally independent patch.
D2557 is also related with this patch, so to test working fine,
need to install those all three patches.

1. _elm_interface_scrollable_content_region_show store wx
   into scroll_interface_data without coverting mirrored_x.
   fix to store wx to mirror-converted x if is_mirrored.

2. _elm_scroll_x_mirrored_get return mirroed_x after compare zero not minx.
   so current mirrored_x couldn't be less then 0.
   fix to check min not 0 for set return value.

3.  _elm_scroll_x_mirrored_get calculation need to consider start position of scroller.
some scroller(e.g. gengrid) start from non-zero position, so calculation need to change
like below.
ret = (cw - (x + w - min));

@fix

Test Plan: You can test this after merge D2553 patch and D2557 and test gengrid2.

Reviewers: raster, Hermet, seoz, jaehwan, tanwar.umesh07, cedric

Subscribers: tanwar.umesh07, Jaehyun, anand.km, eagleeye, singh.amitesh

Differential Revision: https://phab.enlightenment.org/D2558

Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>